Session: 08-05-01 Internal Flows & FIV

Paper Number: 124537

124537 - Experimental and Numerical Investigation of the Inlet Effect on the Dynamics of a Water Intake Pipe 

The water intake pipe/riser has been widely adopted in several engineering applications, such as deep seawater utilization, Ocean Thermal Energy Conversion (OTEC), and the cooling system for FLNG. Its structural characteristics have been regarded as a hanging-off riser with significant research outputs in structural dynamics and Vortex-Induced Vibration (VIV). However, several experimental results suggest that the internal flow velocity at sufficiently large values plays a substantial role in its global behavior and stability. As with VIV, self-induced vibration due to the internal flow has been consistently reported as a design concern. Furthermore, even if the internal flow does not lead to instability, the high internal flow velocity could change the response characteristics and cause unpredictable resonances and lock-in events under an external cross flow or a motion excitation at the top connector.

An internal flow effect on a flexible pipe has been mainly studied from the fundamental perspective as the discipline of a “pipe conveying fluid”. The water intake pipe has been systematized as aspirating pipes, with several studies focusing on its instability. An essential aspect of an aspirating pipe is that the inlet flow at the pipe tip strongly affects the global dynamics of the pipe, not just the internal suction flow. Previous interpretations of the inlet effect of the pipe aspirating water have been limited in explaining the experimental results as in OMAE2023-103375 (Hisamatsu and Utsunomiya, 2023).

This study aims to provide data and physical insights into the inlet effect of the water intake pipe/riser. This paper reports a numerical simulation of the flow field at the pipe inlet and a tank experiment using different inlet shapes.

We performed CFD numerical simulations using OpenFOAM (v2212). Velocity and pressure distribution around the entrance of the pipe subject to sinusoidal motion are analyzed by employing the URANS solver and the dynamic mesh function. Then, the hydrodynamic forces acting on the macroscopic inlet zone are further evaluated, and their effects on the global dynamic characteristics of the water intake pipe are discussed.

  The tank experiment was conducted in the deep water tank at the Research Institute for Applied Mechanics (RIAM), Kyushu University. This experiment used a polycarbonate pipe with a length of 4 m and an inner diameter of 0.02 m. We measured the motion with/without internal flow velocity by selecting a value of 5.5 m/s and sinusoidally exciting the top end of the pipe. Also, this paper investigates the effect of different inlet shapes: cutted-shape, bell-mouth, T-junction, and elbow. The later part of this paper discusses the inlet shape effects regarding the stability, frequency response, and lock-in perspectives.

Presenting Author: Ryoya Hisamatsu Kyushu University, Department of Maritine Systems Engineering

Presenting Author Biography: Ryoya Hisamatsu is an assistant professor of the Department of Marine Systems Engineering, Kyushu University, Japan. He received his Ph.D. degree on design methods of an Ocean Thermal Energy Conversion (OTEC) from Kyushu University. His research interests include hydrodynamic loads, flow induced vibration and global dynamic analysis of offshore structures.

Authors:

Ryoya Hisamatsu Kyushu University, Department of Maritine Systems Engineering
Yusei Yamaguchi Kyushu University, Department of Maritme Engineering
Carlos Riveros-Jerez Universidad de Antioquia, Faculty of Engineering
Tomoaki Utsunomiya Kyushu University, Department of Marine Systems Engineering